My own personal take, because I really dislike confrontation overall, is that respect of Players choices for their characters and GM reasons for their restrictions be taken seriously during a session zero. And if a session zero is not possible, then a mutual coming together should be found. A reasonable GM can work an odd ancestry into a campaign, and a reasonable player can help this take place by talking with the GM about how to do so. And I'm talking about campaigns where anything can and should go, let's face it, we are here to play out stuff that we think would be fun.
I've got a tonne of Pathfinder 2e stuff, and well, there's a HUUUUUGE number of wild ancestries available. And these funky cool ancestries also have a rarity value of either uncommon or rare to help guide both sides of the table.
If your table of players, at the end of a session zero, all end up with rare ancestries, one of each type, well that's perfectly fine, but as the GM, you can define guidelines beforehand if you want players to limit their choices, however, I do get the "double take" looks that can occur when there's is a high mix of these types of parties because I find them interesting and go "how is this going to work? Will be interesting to find out!"
Also, what's the level of immersion? I have played in some games where I am full RP'ing my rare ancestry, but three sessions later, well, I'm just playing a strangely skinned human. I've also GM'd games where I have a set of guides and then, a few sessions in, a bunch of those guides have been either dropped or massively warped, because the fun of the table at the time meant altering them. And I've been lucky that people I have played with have been cool about it too.
I like to be accommodating, and yeah, maybe it's a bit of the old "peace, love, and mung beans" approach, but there's enough RL conflict out there without bringing that stuff into my table. You want to play an undead skeleton in a campaign set in a holy land with strict deity laws about the undead, then let's work out how your character is going to work...
